This invention relates to combustors in combustion turbine engines and, specifically, to the cooling of combustor components, such as the liner, in such engines.
Conventional gas turbine combustion systems employ multiple combustor assemblies to achieve reliable and efficient turbine operation. Each combustor assembly includes a cylindrical liner, a fuel injection system, and a transition piece that guides the flow of the hot gas from the combustor to the inlet of the turbine. Generally, a portion of the compressor discharge air is used to cool the combustion liner and transition piece, and is then introduced into the combustor reaction zone to be mixed with the fuel and burned.
In systems incorporating impingement cooled transition pieces, a hollow impingement sleeve surrounds the transition piece, and the impingement sleeve wall is perforated so that compressor discharge air will flow through the cooling apertures in the sleeve wall and impinge upon (and thus cool) the transition piece. This cooling air then flows along an annulus between the sleeve surrounding the transition piece, and the transition piece itself. This so-called “cross flow” eventually flows into another annulus between the combustion liner and a surrounding flow sleeve. The flow sleeve is also formed with several rows of cooling holes around its circumference, the first row located adjacent a mounting flange where the flow sleeve joins to the outer sleeve of the transition piece. The cross flow is perpendicular to impingement cooling air flowing through the holes in the flow sleeve toward the combustor liner surface.
The presence of this cross flow negatively impacts the cooling effectiveness of the impinge coolant entering through the impingement sleeve and the flow sleeve. This effect is greater as the coolant moves toward the forward end of the combustor because of the increased cross flow through the annulus and has a particularly strong influence on the cooling effectiveness in the zone near where the first row of jets in the flow sleeve would have been expected to impingement cool the combustor liner. Specifically, the cross flow impacts the first row of flow sleeve jets, bending them over and degrading their ability to impinge upon the liner. In addition, the cooling effectiveness of the cross flow itself is reduced once the flow assumes an almost purely axial flow direction, which tends to occur as the coolant moves toward the forward end of the combustor and into the annulus surrounding the liner.
The low heat transfer rate can lead to high liner surface temperatures within the liner and transition piece and, ultimately, loss of material strength. Several potential failure modes due to the high temperature of the liner include, hut are not limited to, cracking of the aft sleeve weld line, bulging and triangulation. These mechanisms shorten the life of the liner and/or the transition piece, requiring replacement of the part prematurely. As a result, there is a need for improved cooling systems in this region of the turbine.